Systems for Light Detection and Ranging (LIDAR) are attracting a great deal of interest because of their numerous applications in fields such as autonomous vehicles, free-space communications, three-dimensional geographic information systems (3D GIS), and electronic imaging. Miniaturization of LIDAR components can potentially make LIDAR even more useful and further expand its range of applications. Integrated silicon photonics is one enabling technology for such miniaturization.
It was recently recognized that phased arrays implemented in silicon photonics technology can be used to steer optical beams, particularly infrared beams. In one approach, a grating diffracts an optical beam, wavelength tuning is used to steer the beam along one axis, and phase control is used to steer the beam along the orthogonal axis. Such an approach is described, for example, in the following publications: K. Van Acoleyen, H. Rogier, and R. Baets, “Two-dimensional optical phased array antenna on silicon-on-insulator,” Opt. Express 18(13), 13655-13660 (2010); and J. K. Doylend, M. J. R. Heck, J. T. Bovington, J. D. Peters, L. A. Coldren, and J. E. Bowers, “Two-dimensional free-space beam steering with an optical phased array on silicon-on-insulator,” Opt. Express 19(22), 21595-21604 (2011). Further, the use of thermo-optical tuning in a phased array of dielectric grating elements is described, e.g., in J. Sun, E. Timurdogan, A. Yaacobi, E. Shah Hosseini, D. Coolbaugh, and M. R. Watts, “Large-scale nanophotonic phased array,” Nature (London), 493, 195-199 (2013).
In another approach, chip-scale silicon photonics technology is integrated with a metallic nanoantenna element array. An array of nanoantenna elements scaled for near-infrared emission are fed by silicon waveguides and subjected to individual thermo-optical phase control for steering a surface-normal beam. Such an approach is described, for example, in C. T. DeRose, R. D. Kekatpure, D. C. Trotter, A. Starbuck, J. R. Wendt, A. Yaacobi, M. R. Watts, U. Chettiar, N. Engheta, and P. S. Davids, “Electronically controlled optical beam-steeling by an active phased array of metallic nanoantenna elements,” Opt. Express 21, 5198-5208 (2013), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-4-5198, the entirety of which is hereby incorporated herein by reference.
The nanoantenna element array can in principle steer a beam over an extremely wide angle, approaching 180°, using waveguide thermo-optic heaters to control the individual phases of the respective nanoantenna elements. However, the pitch of the nanoantenna elements is limited by the presence of an individual phase-shifter for each of the nanoantenna elements. This limits the steering angle that can be achieved in practice.
An improvement is described in U.S. Pat. No. 9,104,086 (hereinafter, “the '086 patent”), commonly assigned herewith, which issued on Aug. 11, 2015 to Paul Davids et al. under the title, “Method and Apparatus of Wide-Angle Optical Beamsteering from a Nanoantenna Phased Array,” the entirety of which is hereby incorporated herein by reference.
The above-cited U.S. Pat. No. 9,104,086 describes a chip-scale device in which the nanoantenna elements are arranged in a two-dimensional array of rows and columns. Within each row, the thermo-optical phase elements are treated in aggregate by heating them uniformly with a single controllable heating current. Thus each phase element can be implemented, for example, as a portion of a silicon waveguide that underlies a particular one of the nanoantenna elements. If, e.g., the nanoantenna elements are equally spaced relative to propagation length along the waveguide, then at any given uniform temperature there will be an equal phase shift between successive nanoantenna elements of the row.
The uniformly distributed phase shift is sufficient for steering the emissive plane of the row. A plurality of rows is arrayed along the column direction to provide steering in the orthogonal dimension. By eliminating the individual phase-shift elements in each row, the pitch limit can be overcome and nanoantenna element spacings can be achieved that make beam steering possible over a substantially greater range.
Still further refinements can lead to implementations that offer very wide apertures, multiple beams, and other useful features.